This invention relates generally to the in situ repair of underground pipe systems, and more particularly to a trenchless method (no excavation) of repairing in-place holes, cracks and defective joints in underground gravity flow pipe systems, such as municipal and industrial sewer systems.
The integrity of underground pipe systems, particularly sanitary sewer systems, is a matter of substantial concern to urban communities. Sanitary sewer systems are designed to convey raw sewage and wastewater to treatment facilities where the sewage is processed and the wastewater is treated for return to the environment. Ideally, the sewer system will convey the raw sewage and wastewater to a treatment facility without leaking or spillage. Due to age and numerous other causes, however, present day urban sanitary sewer systems are in a state of disrepair. Most of these systems have cracks, holes, and open joints in the sewer mains which are generally buried beneath streets. Defects in the lateral pipes, which extend from private buildings to the sewer mains, cause even more problems. Also prevalent are poor or no joint seals between the adjacent lateral pipe sections, and defective or no joint seals at the connections between the laterals and the sewer mains. These defects can cause serious concern for the communities in which they appear. Defects such as breaks, cracks, or open pipe joints, allow storm water and ground water to infiltrate into the sewer system and, under some conditions, to overload the waste water system. One result is that the rain water and ground water infiltrating into the sewer system must be treated, just as the wastewater and raw sewage must be treated, at a substantial, unnecessary expense to the community. Another result of such defects in sewer systems is that raw sewage is allowed to escape from the system into the surrounding earth where the ground water becomes contaminated and a sanitary problem is created. Also, during rainy weather the rain water entering the sewer system can overload the treatment facilities causing untreated, raw sewage to be discharged into neighboring rivers, lakes and streams. The escape of raw sewage from defective pipes; the overloading of sanitary treatment facilities; and the consequent dumping of untreated or improperly treated raw sewage directly into rivers, lakes and streams causes both unsanitary health hazards and ecosystem problems in violation of environmental regulations. Another problem caused by the infiltration of ground water into sewer pipe is the continuing deterioration of the buried pipe. When a crack in buried gravity flow pipe allows ground water to enter, it typically allows soil particles to enter the pipe. As the soil flows into the pipe with the ground water, a void will form on the outside of the pipe. Because a buried pipe gets much of its stability from the equal pressure of the surrounding soil, a void will cause unequal stress which weakens the structure and leads to additional cracks, breaks, or other deterioration. This in turn causes more soil to be lost by draining into the pipe. If allowed to continue, such voids can cause a total collapse of the pipe. The collapse of the overhead soil around a buried pipe can cause a cave in all the way to the surface. Indeed, many pot holes and sinking areas in city streets are caused by such voids collapsing.
The obvious solution to the problem of defective sanitary sewer pipes is replacement which requires excavation. This solution must be performed substantially in the middle of busy urban streets and is not a practical solution because it is expensive, inconvenient and dangerous. Also, in most instances, it is not the total pipe that needs replacement, but simply a small part or crack or leaky joint therein which requires repair.
The need for a workable trenchless, in-place, non-structural technique for underground pipeline rehabilitation has been a long known problem. Several innovative technologies have emerged which create a structurally new thermoplastic or thermosetting plastic pipe within the existing deteriorated pipe in situ. These techniques, sometimes called sliplining, are one solution to the problem of exfiltration of raw sewage into the surrounding earth, but, generally do not solve the problem of infiltration without excavation. Also, sliplining, and other similar methods, do not fill the existing voids around the pipe; and defective lateral to main connections often remain a problem. The methods of structural repair are expensive, time consuming and, in most cases, not needed to repair isolated cracks and holes or defective joints in the sewer system. Moreover, most of these techniques have the effect of decreasing the pipe diameter, and therefore can reduce the capacity of the system when such systems actually need additional capacity.
A recently completed study of the condition and problems of the sanitary sewers in one large urban area, which is regarded in the wastewater management industry as exemplary of other large urban areas, disclosed substantial deterioration of the pipes and pipe joints and indicates that major efforts and new techniques are needed to rehabilitate, repair, replace or upgrade the sewer system to meet current environmental and public health standards.
Accordingly, there is a need for an inexpensive, non-structural, but effective and permanent in-place rehabilitation technique for selectively sealing isolated holes, cracks and defective joints in sanitary sewer pipe. Attempts have been made and processes have been proposed and described over the years for trenchless, in-place, non-structural underground pipe repair. One early attempt is disclosed in U.S. Pat. No. 1,736,293. This prior process pumped Portland cement grout, under pressure, into an isolated section of the defective pipe to be repaired. The theory is that the grout will be pushed into any cracks or fissures where it will harden and seal the leak. There are several drawbacks to this prior method. Portland cement grout, or other unspecified grouts, will cure, or harden, (a chemical reaction) throughout its entire volume at the same time. This hardening feature will cause plugging of the pipe as well as the leaks. This prior process attempts to avoid the problem of hardening by diluting the main body of the grout with water or other chemicals once it is in place. While such diluting can inhibit curing and hardening of the main body of the grout, it can also dilute and weaken the grout which has been forced into the cracks and fissures to seal the leaks in the deteriorated pipe. Another substantial problem with this prior process has both economic and environmental aspects. Rich Portland cement grout, as used in this prior process, is expensive, and the entire volume of Portland cement grout used to flood the pipe, minus the relatively small amount forced into the cracks, cannot be reused and must eventually be wasted at a substantial economic loss. Another drawback of the grout process is the problem of safe disposal of hundreds, and perhaps thousands, of gallons of used Portland cement or chemical grout waste, creating a potential ecological-environmental problem. Also, Portland cement deteriorates rapidly in an acid environment, and many sewer systems naturally generate sulfuric acid which collects on the walls of the pipe. It is common to see concrete (Portland cement and aggregate) pipe in sanitary sewer systems corroded completely away, where the acid in the system has been in contact with the pipe wall. The Portland cement grout pipe repair process suggested in U.S. Pat. No. 1,736,293 is not a technique that is used in the pipe repair industry.
Another prior process for the in-place repair of underground pipe is disclosed in U.S. Pat. No. 3,227,572, which suggests the use of chemical dispersing agents with a small percentage (0.02%) of wax particles. The process includes the preparation of a dispersion comprised of microscopic particles of solid wax of 0.1 to 2.5 microns. These particles are dispersed throughout a water medium. When the treated water is introduced into the defective pipe, the water containing the microscopic particles of solid wax seeps out through cracks and into the surrounding soil. If the soil is a fine grain soil, it will act as a filter and the microscopic particles of wax will begin to build up in the soil adjacent to the crack in the pipe. Eventually, if internal pressure is continuous and other conditions permit, a wax membrane will be formed. As the wax membrane accumulates and the surrounding soil becomes more and more saturated with water, less and less water will flow through the crack and penetrate the soil, and the membrane growth will slow. Because of the microscopic size of the wax particles, the membrane will not form in gravel or coarse granule soils. The membrane if formed, will be relatively thin and fragile. When the internal pressure is removed, the membrane can be subject to immediate failure from the external ground water pressure. This microscopic wax particle dispersion process may not be cost effective because the entire unused volume of wax particle dispersion within the pipe must be disposed of and, therefore, wasted. Another problem with this wax particle method in a water dispersion is the relatively complicated preparation process for the dispersant as shown by the examples stated in the patent. This microscopic wax particle dispersant method for the in-place repair of underground pipe is not a technique that is recognized or used in the pipe repair industry.
Another prior process for the trenchless, in-place repair of buried pipe is disclosed in U.S. Pat. No. 4,244,895. This method suggests the use of a chemically hardening grout, such as Portland cement. The pipe section to be repaired is isolated and filled with grout under pressure so that the grout is pushed into and through any cracks in the pipe. Then, instead of diluting the grout to prevent internal hardening (as in U.S. Pat. No. 1,736,293 discussed above) the grout is pushed out with water before it sets up, using a sliding plug as a divider to separate the grout and water. This process has the same problems as mentioned in the discussion of U.S. Pat. No. 1,736,293 above, such as diluting the grout which remains in the cracks, or washing all or part of the grout out of the cracks. Also, all of the nonused grout within the pipe will be wasted and must be disposed of in an environmentally approved manner. The Portland cement grout in the cracks will be easily attacked by acids naturally occurring in the sanitary sewer system. A significant problem with this prior method would be getting a sliding plug to separate two different fluids (grout and water) within a deteriorated sewer pipe, with all of its irregular features. This prior process for repairing underground pipe using chemically hardened grout is not a technique that is recognized or used in the pipe repair industry.
There are no effective prior art processes capable of a non-structural, trenchless, in-place repair of sewer main pipe, lateral pipe, lateral pipe joints and the connection joint between the lateral pipe and sewer pipe. There is a need for an efficient, effective, permanent, relatively simple non-structural process for the in-place repair of underground pipe.